Speedometer, particularly for aircraft



394i J. G. PAuLaN fi fi SPEEDOMETERS, PARTICULARLY FOR AIRCRAFT FiledJuly 8, 3.940 5 Sheets-Sheet 1 Nov. 24, 1942. J. PAULIN SPEEDOMETERS,PARTICULARLY FOR AIRCRAFT Filed July 8, 1940 5 Sheets-Sheet 2 Nov. 24,1942. J. G. PAULlN SPEEDOMETERS, PARTICULARLY FOR AIRCRAFT Filed July 8;1940 s Shets-Sheet 5 Patented Nov. 24, 1 942 R SPEEDOMETER, PARTICULARLYFOR AIRCRAFT Josua Gabriel Paulin, Nockeby, Sweden Application July 8,1940, Serial No. 344,439

- In Sweden September 18, 1939 5 Claims. 73-182) The object of thepresent invention is a velocity meter for the measuring of the velocityof flow of a gaseous medium or other medium of variable density flowingpast the meter or relatively thereto, and the invention is particularlyintended to be brought into use for the measuring of the speed of anaircraft relatively to the surrounding air. The speedometer according tothe invention is of the type wherein a pressure of flow or speed createdwithin a Pitot-tube, Venturi-tube or the like is caused to actuate adiaphragm connected to an indicating or pointer mechanism. Since thepressure of flow or speed is, highly dependent on the density of themedium, the deflection of the pointer of a speedometer of thisdescription will be subjected to great variations with the staticpressure unle'ss measures for compensation are undertaken, and in anaircraftsuch pointer deflection will at a constant speed be so much lessthe greater the altitude of the craft is above ground. With anincreasing altitude the static pressure will not diminish linearly butmore rapidly, to begin with, and then more and more slowly. To providefor correction of the wrong indication increasing with the altituderelatively to the reading at the ground, use may be made of a curvediagram indicating thenecessary 'corrections for 'difierent altitudes,but this expedient will be found to be rather inconvenient. It isdesirable, therefore, to provide the speedometer with a compensatingmeans adapted to make correction directly for the, wrong indicationcaused by the change of the static pressure, "so that the proper speed,may be read directly oil the dial of the instrument. v e

According to the present invention, such compensation for the dependenceof the pressure of flow or speed on the density of the medium iseffected by the fact that an auxiliary diaphragm or the like respondingto the static pressure of the medium is connected in a counter-operativemanner to the pointer mechanismthrough a gearing having a variable ratioof gear under the influence of the main diaphragm, that is to say thediaphragm actuated by the pressure of flow,

in a manner such that the ratio of gear is increased with the velocityof flow or speed. Pref erably, the variable gearing consists of twofilaments or links connected pivotally and preferably at an obtuse anglewith each other, one end of 7 the filament or link system beingconnected to the auxiliary diaphragm, and the other end and the apex ofthe angle being connected to the main diaphragm and the pointermechanism respecabove, the compensating means is so constructed that the,correction of the pointer deflection brought about for a certain changeof the static pressure is so much greater the greater speed is, which isall in agreement with the requirements set up. a

The invention will be described more closely with reference to theaccompanying drawings which illustrate three diflerent forms ofembodiment of speedometers adapted for the measuring of, thespeed of anaircraftrelatively to the air.

closed casing I.

In the embodiment shown in Figure 1, the parts of the speedometeraremounted within a casing l is a system of series-connected aneroiddiaphragm boxes '2, the interior of which may be connected in a mannerknown per-se to a Pitot-v tube by means of a tubing threaded onto a pipesocket or nozzle 3 depending from the casing.

This aneroid system represents the main diaphragm system responding tothe pressure oi speed. The interior of the casing, that is to say theair about the diaphragm boxes,'may be connected in a manner likewiseknown per se to a suitably selected point of the Pitot tube system bymeans of a tube joint connected to thenozzle 4, so that the pressurewithin the casing is maintained equal to the prevalent externalatmospheric pressure. Mounted to the right within the casing is anauxiliary diaphragm box -5 responding to this atmospheric pressure. Abell crank lever 8 mounted in the frame as at 1 is connected to the maindiaphragm system 2 by means of a pin 6. In a like manner, a bell cranklever l0 mounted in the frame at 9 is connected to theauxiliarydiaphragm system 5 by means of a pin connection II. If desired,,shortlinks may be arranged between each diaphragm system and the appertainingbell crank-lever, although the diaphragms 40 generally possesssuillcient flexibility. to yield to the tendency toward breaking ondeflection. The

upper ends of the levers 8 and II) are. interconnected by means of twocoherent flexible bands or filaments l2, l2, which are stretched at an'obtuse angle mutually by the fact that a further flexible-metal band orthe like l3 connecting the point of union of the ribbons l2, l2 with theone arm of a bell .crank lever l5 mounted in the frame at M is alwayskept taut-by means of a spring l5 acting upon the bell crank lever. Thebell crank lever I5 is provided with a balancing counter-weight. l6, andis connected in known manner to a pointer by means of a link IT, atoothed sector l8, and a gear wheel l9, the point tively, or vice versa.As will appear from the of said pointer moving overa dial 2|.

Arranged on the bottom ofthe 'I 'he band system-l2, l2" l3 maybe said torepresent a variable gearing connected intermediate the auxiliarydiaphragm ,box and. the pointer mechanism, the ratio'of gear of suchgearing augmenting according as the obtuse angle between the bands l2and I2 iricreases' It the air craftis moving obliquely upwardly at aconstant in the .instrument is demanded. To. this end rate of speed, sothat the static, pressure will consequently ..diminish successively, theaneroid system 2 will be coin-pressed by'reason ofthe lessened pressureof speed, the bell crank lever 8 being thus. turned in a clockwisedirection. II the right hand end of theband system l2, I2-" were fixed,the obtuse angle between the bands l2 and. I2 would be decreased, and inspite ofthe speed being kept constant-the pointer would.

then indicate'lower and lower values of speed. on account ofthe reducedstatic -pres,sure however, the aneroid box 5- will expand so that thebell crank lever I0 is turned ina clockwise direction, and the righthand end of the band system l2, I2 is moved to the right. If the righthand ends of the two'bellcrank levers are then moved to theright by thesame amount, the angle or the band system will be kept unaltered and thepointer remains practicallyunactuated. If, in-

" stead, the aircraft is moving obliquely down- .wardly at a uniformspeed, the two bell crank levers 8 and ID will conversely be turned in acounter-clockwise direction, while the obtuse angle remainsapproximately unchanged, .as before.

The greater the constant speed, the tauter will the band System12, "I!"be, that is' tosay, the t more obtuse is the angle formed by the twobands. On the other hand, as stated above, the 'ratio' of gear'witl'iwhich the aneroid boxj'actuates the various means known per se may bebrought into use. In the embodiment a'ccording'to Figure 2, both ofthebands or filaments l2; l2 stretched at an obtuse angle to each otherin Fig. 1 have been replaced by two rigid links designated 12:; andI2'a, said links being here connected directly between the auxiliarydiaphragm. box! and thebell crank lever 15a of the pointer mechanism.

The; obtuse apex of the angle is connected to the main diaphragm system'2 through a short link I3 as at 6. The main diaphragm system 2 'is inturn connected directly to the lever. ISa of the pointer mechanismthrough a link. 22'. 0therwise, the arrangement is similar to that inthe previously described case.

Whereasin Figure 1, theband system l2, l2, l3 constitutes a connectionto the pointer mechanism' which is common to the main diaphragm system 2and the auxiliary diaphragm system 5, and is adapted to transfer themovements of both diaphragm systems to the pointer mechanism, the-linksystem I211, I2'a ot Figure 2, on

theother hand, only iorms, a variable-gearing I for ,the auxiliarydiaphragm system, while a certain link 22 serves totransfer themovements of the main diaphragm system to the pointer mechf anism. Theconnection through the link I: be-

tween the main diaphragm system and the.,ob'

- tuse apex of the angle serves to bring about the change or the ratioof gear according to the 1 invention between the auxiliary diaphragmsyspointer is so much greater the more obtuse said I angle is. From thisit consequently follows that the correction of the pointerdeflectionobtained for] a certain definite change or the static pressurewill be so much greater. the-greater thespeed of the.air craft is,'which is a necessarycondition for the correction becoming true. If

' desired, the bands l2,

- 'byrigidlinks.

l2 l3 may replaced Aswill be seen iromthe drawings, the upwardlyprojecting arm otthe bell crank lever Ill isposie tioned obliquely withrespect .to the band I2. con- I nected therewith, in a manner such thatthe direction-thereoi approaches the direction .oftheband inthe sameproportion as the speed de-.

creases, whereby the said ratio of. gear at which the \auxiliarydiaphragm box 5 actuates the pointer mechanisin is renderediurtherdepend ent upon the speed. By this means a more accurate compensation-ismade pos'slble within'the wholemeasuring range. By" suitablyselectingthemagnitude of the obtuse angle forzero speed tem and 'the pointermechanism in dependence on the speed. I

When at an increasing speed the aneroid boxes of the main diaphragmsystem are expanded, the lever 1-51: is .caused to be turned in acounter clockwise direction through thejagency of the link 22.. At thesame time the link [3 raises the 'point of union'between the links Inand l2'a,-

whereby the resulting'moinent arm by which the auxiliary diaphragmsystem *5 actuatesthe pointer mechanism is diminished. Thus a similarresuit will be obtained as according to Figure 1, i-. e. that the ratioof gear between'the auxi liarydiaphragm system and the pointer mechanismis augmented at an increasing .speed,

whereby the magnitude 'of the correction is au mented with the'speed inaccordance with' the requirements. By the successive straighteningouteflect which'the linkage 'system..l2a, l2'a is' subjected" to at anincreaslng'speed theauxiliary diaphragm box will obviously be compressedto" somev extent even if the static pressureshould be.

constant in th, meantime, but this does notengtail' any practicalinconvenience.

speed Whichatht? craft iscapable ot'holding, for

instance 10.0 kilometers per hour, and also-at the rn'aximum' speed.Between the? corresponding,

. points on the dial the latter may-be divided ap proximatelyuniformlyat a suitable ratio of gear of the pointer'm'echanism-itselfl Since thepressu're'of -eetl created within the Pitot tube .does not riselinearlyIWit-hthe' speed, "and sinpe by reas'on of-this.it mi'ght bedimcult to attain a linear correlationbetweenjs eed andpointerdeflection; further compensating means If the static, pressure fallswhile the'cra'ft is moving at a constant rate of speed, the maindiaphragm boxes Twilltend to contract, whereas the auxiliary diaphragmbox 5 tends to-exp'and.

qwi'th proper adjustment 'o'f the link system and of the lengths ofthose moment arms by which. the two diaphragm systems act .upon thepointer mechanism both of said tendencies baiance one anothen'and'the.pointer remains unactuate'd by I the change of-the'air'pressure;

The embodiment according to Figure a-differs from that :shown'in Figure2 only in that the movements of each diaphragm system 2 and. 5

respectively are "transferred to the 'lihk'system I 20,, l2'a, l3through-the'i'ntermediary of somewhat obliquely positioned links 24'and'26 re- I I s'pectively mountedin-the frame and connected may becomenecessary. where any greateccuracy *1 approximately at the centerthereof with the ap-' pertaining diaphragm through short links, 23 and25 respectively. By suitably choosing the length and the obliquity ofthe additional links it will be said flexible members being connected atits outer end to said compensating member, and a spring biasing saidindicator device so as to maintain medium having a pressure-dependentdensity in combination, a measuring member responsive to the flow ofmedium, an indicator device, a compensating member responsive to thestatic pressure of said medium, a transmission device consisting ofthree links connected together at a common center, two of said linksbeing connected at their outer ends to said measuring member and saidindicator device respectively, and the third of said links beingconnected at its outer end to said compensating member in such mannerthat the movement of the compensating member upon increase of staticpressure tends to reduce the magnitude of the indication of flow.

2. In an instrument for measuring the flow of a medium having apressure-dependent density in combination, a measuring member responsiveto the flow of 'medium, an indicator device, a

compensating member responsive to the static pressure of said medium. atransmission device consisting of three elongated flexible membersconnected together at a common center, two of said flexible membersbeing connected at their outer ends to said measuring member and saidindicator device respectively, and the third of said flexible members instretched condition, the interconnection between said third flexiblemember and said compensating member being so devised that the movementof the compensating member upon increase of static pressure tends toreduce the magnitude of the indication of flow.

3. In an instrument for measuring the flow of a medium having apressure-dependent density in combination, a measuring member responsiveto the flow of medium, an indicator device, a compensating memberresponsive to the static pressure of said medium, a lever operativelyconnected with said compensating member, a transmission deviceconsisting of three links connectedtogether at a common center, two ofsaid links being connected at their outer ends -to said measuring memberand said indicator device respectively, and the third of said links be-.ing connected at its outer end to one arm of said lever in such mannerthat the movement of the compensating member upon increase of the staticpressure tends to reduce the magnitude of indidication of flow and thatthe direction of the said lever arm approaches the direction of the linkat diminishing velocity of flow.

4. An instrument according to claim 1, in which a lever isinterconnected between the measuring member and the transmitting device.

5'. An instrument according to claim 1, in which a lever isinterconnected between the indicator device and the transmitting device.

'JOSUA GABRIEL PAULIN.

